This is my first large powerboat and, watching the chatter on this and other forums, I notice many owners use golf cart batteries for house banks. Just curious if there are specific reasons for using GC batts. rather than standard 12V heavy duty deep cycle types: Cost, deep cycle capacity, recharge time...?
Joe C.

Most 12V batteries labeled "deep cycle" are not. They are made no differently from the manufacturer's starting batteries- just a different label. One easy clue: any 12V battery that doesn't have an amp hour rating particularly one labeled on the outside is not a deep cycle battery.

Here are some features and benefits of GC batteries:

1. Heavy plates. Deep cycle batteries with their hundreds of cycles of discharge/charge can eat through the plates of normal starting batteries.

2. More room in the bottom for sludge. Sludge, sloughed off sulfates, can build up on the bottom and ultimately short the plates.

3. Fill caps. You can add water if needed (shouldn't need to do it more than 1-2 times a year with modern chargers) and check the specific gravity which is an accurate measure of state of charge.

4. Any GC battery manufacturer who doesn't build them this way will be quickly run out of business. There are millions of GC batteries sold annually and the users understand what it takes to perform right.

Now AGMs are different and there really isn't any difference in construction between a deep cycle and a starting battery. But they cost twice what a GC battery costs for the same amp hours.

Because 12 v wet batteries are damaged if allowed to fall below a half charge, a battery rated at 230 amp/hrs is really only a 115 amp battery. Replace it with 2 golf carts rated at 230 amps and you actually get 230 amps.

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GC batteries tend to have long lives with number of cycles typically far exceeding what most boat cruisers would utilize. When comparing them to other battery chemistries such as AGM, they are very low cost to replace provided you have the old batteries to turn in as cores. I find this very desirable should I want to do a year long trip, I can decide to replace older but maybe not spent batteries before leaving, at a tolerable price. With more expensive chemistries, it's tougher to justify changing out before they die.

Ted

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Because 12 v wet batteries are damaged if allowed to fall below a half charge, a battery rated at 230 amp/hrs is really only a 115 amp battery. Replace it with 2 golf carts rated at 230 amps and you actually get 230 amps.

I have never used golf csrts, but thought they were six volts. If this is correct, then two batteries rated at 230 amps will provide 230 amps at 12 volts., providing only 115 useful Amps on the end.

To be clear. 12v deep cycle batteries are going to give you about 105 amp hours but you can only use about half that. GC batteries are 6v, you need two for 12v use. You are going to have 230 amp hrs for which you can use about 70%.

Two - 12v batteries at 105 ah each = 210 of which you can use .5 = 105 useable.
Two - GC batteries at 230 ah each = 230 at 12v of which you can use .7 = 160.

My boat originally had 2 8Ds for the house. They are very heavy and are in a terrible location to swap out. I use 4 6V golf cart batteries in place and get the same amp hours. They are much easier to swap, although still very difficult to do. You wire two each in series and then wire the two series sets in parallel to get the 12V. There is a specific way to wire them in order to fully utilize the batteries.

I went with Lifeline 6v 230ah AGM batteries based on specs and recommendations from experts, plus experience I've had with them. Four of them yield a net of 230ah of power, which for an overnight on the hook, provides the power I need all night long and into the next day before I crank my engine a head out.

I'm not sure if GC batteries are the only true deep cycle batteries out there. Maybe manufacturers do just print different labels. But, I guess I'd want to be sure we are distinguishing true deep cycle batteries from dual-use batteries.

Regardless, here are the reasons I like golf cart batteries for the house batteries:
1) Cheaper per 12V amp-hour than other deep cycle batteries.
2) Easier to carry onto and off of the boat than larger batteries.
3) If a cell goes bad, I have to replace only a smaller cheaper GC2 battery, rather than a larger, more expensive battery (that is basically like the GC2 packed in one).
4) Sometimes more options to squeeze smaller boxes into nearby spaces than comparable larger battery box(es).

Down side(s) to GC2 batteries as compared to /large/ 12V batteries, e.g. 8Ds:
1) Even though 2 GC2 batteries fit in a box, larger batteries tend to waste less space per box, because of the "extra" space around each battery in the boxes. So, I think larger battery boxes have more energy per box volume.
2) Tying 6V batteries together takes more wiring. This is true both for the "jumpers" to combine the 2x6V batteries in series into one 12V battery, and then the wires needed to tie multiple of those together in parallel. This is more time spent cutting and crimping. And more posts to keep clean of corrosion. And, more crimped connectors that can corrode or weaken from mechanical stress. And more clamp connectors that can loosen.
3) There are more boxes to open and close to check water as compared to larger 12V batteries.

All-in-all, I am a fan of the GC2 approach. Mostly because of the price per A-Hr. But, my current boat has 4D dual-use batteries. When they go, I'll probably replace them with deep-cycle house batteries if I can find them. I don't know where I'd put a bunch of GC2 in boxes.

Of course, if you aren't going to box the batteries, that does change things a lot.

"But, I guess I'd want to be sure we are distinguishing true deep cycle batteries from dual-use batteries."

The fastest method is to read the label , if there is a CCA or phony MCCA rating its probably not a true deep cycle batt. Probably a dual use. A deep cycle will use a "20 hour rate" to size the batt amps available.

Like everything quality counts , although there are only a few batt mfg , I would pay extra for a Trojan or Surette DC than an unknown brand from Costco.

50% SOC is the point where further discharge costs a bit more in batt life , but going to say 30% DOD will not kill the batt , just shorten the number of cycles it can stand before needing replacement.

Trojan has a chart .

Most cruisers will install more batt than required as constant undercharging (not getting to 100%SOC after every discharge ) also costs battery capacity.

With a proper V regulator and good sized Alt, 85% SOC can be pretty fast , esp if the V reg has a temperature input, but from 85% to 100& can be an eternity.

Eventually the batt will be "smaller" in terms of amp hours it can give , no big deal as long as you are prepared for the capacity drop.

Solar is a great help in getting to 100% SOC.

A SOC meter is required to understand where the batt is in terms of charge.A Volt meter almost useless.

My main reason for using GC’s (8 of them for 2 banks) is that I am no longer a young teenager strong enough to lift out a group 4 or 8 alone. Sure there is extra wiring along with more cells to check for fluid levels.

Added wiring time is not a concern nor is the fluid checking. With a decent 3 stage charger plus in my case a Victron 150-70 controller for my solar, I found checking/adding water just once a season is enough.

A weekly water requirement suggests several bad cells. A bad cell will cause the nearby cells to work harder. An infrared gun would show different temperatures in the different cells. The result would be some warm cells off gassing the battery fluid continuously requiring frequent refilling.

Batteries are damaged when fluid level gets low exposing the lead plates.

my First thought is you have bad batteries. However, you have not given any info about your battery charger. Is it a very old charger or a newer modern charger?

The battery's are definitely toast, someone had suggested that my system as overcharging. However I think the water level ran low they were damaged. I was replacing them this year either way. Local battery shop in town is where I have been directed to go by the dock veterans.

Suspect the charger was the original '01. Will look again once the snow bank melts and I have access.